Servo control circuit for detecting analytes via nanoparticle-labeled substances with electromagnetic read-write heads

ABSTRACT

A circuit for controlling an electromagnetic head module to detect antigens on a biosample track comprising a processor for receiving position-error-servo signal from the PES read sensor, a write head for magnetizing nanoparticles attached to antigens, and a read sensor for detecting the nanoparticle-labeled antigens. The circuit may further comprise an X-axis actuator for controlling the head module in the direction perpendicular to the track and an Y-axis actuator coupled to the head module and the X-axis actuator for controlling the head module in the direction of the track. Target antigens are attached to the biosample track and nanoparticles via antibodies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalPatent Application Ser. No. 61/246,329, entitled “READ-AFTER-WRITEDETECTION OF ANALYTES VIA NANOPARTICLE-LABELED SUBSTANCES” filed on Sep.28, 2009, and is related to co-filed, co-pending and commonly assignedU.S. patent applications: Ser. No. 12/888,388 entitled “DETECTION OFANALYTES VIA NANOPARTICLE-LABELED SUBSTANCES WITH ELECTROMAGNETICREAD-WRITE HEADS”, Ser. No. 12/888,394 entitled “READ-AFTER-WRITEDETECTION OF ANALYTES VIA NANOPARTICLE-LABELED SUBSTANCES”, and Ser. No.12/888,408 entitled “A CIRCUIT FOR DETECTING ANALYTES VIANANOPARTICLE-LABELED SUBSTANCES WITH ELECTROMAGNETIC READ-WRITE HEADS”,all of which are hereby incorporated by reference.

BACKGROUND

The invention relates to analytical devices and processes, and moreparticularly, to devices and processes that incorporate electromagneticwrite-heads and magneto-resistive read-sensors to detect analytes viananoparticle-labeled substances.

It is known that antibodies bind with antigens as part of the humandisease defense system. Presently, antigens are detected by suchtechniques as immunofluorescence, immunoperoxidase, or enzyme-linkedimmunosorbent assay (ELISA), each of which then employs a microscope forvisual detection of the target antigen. It is desirable to exploit theuse of magnetic signaling technology to automate the detection ofanalytes, such as antigens, and to further apply this technology to thedetection of any biological matter.

BRIEF SUMMARY

A first set of antibodies are bonded to a substrate, then this first setof antibodies are exposed to and bonded with target antigens. A secondset of antibodies are bonded to demagnetized nanoparticles, and thesenanoparticle labeled antibodies are exposed to the target antigens. Thenanoparticles are then detected by the use of magneto-resistiveread-sensors. Examples of read-sensors include anisotropicmagneto-resistive (AMR), giant magneto-resistive (GMR), and tunnelmagneto-resistive (TMR) read-sensors.

In an exemplary embodiment of the invention, an electromagneticwrite-head first magnetizes the nanoparticles, and then amagneto-resistive read sensor, such as an AMR, GMR, or TMR read-sensor,detects the freshly magnetized nanoparticles.

In another exemplary embodiment, the first set of antibodies may bebonded to biosample tracks deposited on a substrate. The substrate maybe a flexible film of polyethylene terephthalate (PET), such as used inconventional magnetic tape, or other polymeric film. Alternately, thesubstrate may be glass, or may be a Peltier material to allow selectiveheating and cooling of the substrate and the biological sample on thesubstrate.

Nanoparticles of differing magnetic properties are selectively pairedwith antibodies associated with different antigens, so that multipletypes of antigens can be simultaneously detected upon a single scan ofthe read-sensor.

For a fuller understanding of the invention, reference is made to thefollowing detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a top view of an analytic device accordingto an exemplary embodiment of the invention.

FIG. 2 is a block diagram of an exemplary Z-pattern servo-alignment markaccording to an embodiment of the invention.

FIG. 3 is a block diagram of a side view of an exemplary analytic deviceaccording to an embodiment of the invention.

FIG. 4A is a flow chart illustrating an exemplary analytic processaccording to an embodiment of the invention.

FIG. 4B is a continuation of the flow chart in FIG. 4A, illustrating anexemplary analytic process according to an embodiment of the invention.

FIG. 5 is a flow chart illustrating an exemplary process for calibratinga read-sensor for use in detecting nanoparticle labeled antigens,according to an embodiment of the invention.

FIG. 6 is a block diagram of an exemplary circuit for controlling theX-axis and Y-axis motion of the head-module of an analytic device,according to an embodiment of the invention.

FIG. 7 is a block diagram of an exemplary write and read circuit for usewith an analytic device, according to an embodiment of the invention.

DETAILED DESCRIPTION

The invention is described in exemplary embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. While the invention is describedin terms of the best mode for achieving the invention's objectives, itwill be appreciated by those skilled in the art that variations may beaccomplished in view of these teachings without deviating from thespirit or scope of the invention.

Referring to FIG. 1, there is illustrated a top view of an examplesubstrate 199, which may comprise a Peltier hard-substrate, a glasssubstrate, a polyethylene terephthalate (PET, which is commonly known bythe trade name of Mylar™) flexible-substrate, or other materials havingsimilar properties. In an exemplary embodiment of the invention,head-module 104 scans across stationary substrate 199 fromleft-to-right, along the +Y-axis, individually sampling one orsimultaneously sampling a plurality of biosample tracks 180.Alternately, substrate 199 may be swept across stationary head-module104 from right-to-left, along the −Y-axis. If substrate 199 is of aflexible polyethylene terephthalate material, then in one embodiment,this right-to-left motion may be performed as data read-write operationsin a magnetic tape drive. As an alternate embodiment of the invention,head-module 104 comprises a helical-scan rotary head-module, and theY-axis of the biosample tracks 180 is at an angle to the substrate.

FIG. 1 shows electromagnetic write-heads 106 and magneto-resistiveread-sensors 108 arranged in pairs in head-module 104. Theelectromagnetic write-heads 106 first write to biosample tracks 180, andthen the adjacent magneto-resistive read-sensors 106 immediately readfrom biosample tracks 180, which is referred to as a read-after-writeoperation. In an exemplary embodiment of the invention, substrate 199comprises eight biosample tracks 180 corresponding to eight bits in abyte, and hence to eight electromagnetic write-head 106 andmagnetoresistive read-sensor 108 pairs in a typical head-module 104 usedin magnetic tape drive products. However, as alternatives, any number ofbiosample tracks 180 may be used. The number of electromagneticwrite-head 106 and magneto-resistive read-sensor 108 pairs inhead-module 104 may be any number ranging from a minimum of one to thenumber of electromagnetic write-head and magneto-resistive read-sensorpairs in the head-modules of the tape drives. For example, there aresixteen such electromagnetic write-head and magneto-resistiveread-sensor pairs in a head module of an IBM 3480™ tape drive.Typically, the number of biosample tracks 180 is an integral multiple ofthe number of write-head 106 and read-sensor 108 pairs. In an alternateembodiment, a single device may perform the functions of both thewrite-head 106 and read-sensor 108.

Write-heads 106 may comprise miniature electromagnets, with a coilsandwiched between to poles, such as taught without limitation by U.S.Pat. No. 5,452,164, entitled “Thin Film Magnetic Write-head,” which ishereby incorporated by reference in its entirety. Write-heads 106 maycomprise other structures with similar functionality.

Read-sensors 108 may be anisotropic magneto-resistive (AMR), giantmagneto-resistive (GMR), or tunnel magneto-resistive (TMR) read-sensors,or other devices having similar functionality. AMR read-sensors aretaught without limitation by U.S. Pat. No. 5,005,096, entitled“Magnetoresistive Read Transducer Having Hard Magnetic Shunt Bias,”which is hereby incorporated by reference in its entirety. AMRread-sensors may comprise other structures having similar functionality.GMR read-sensors, which are also known as spin-valve read-sensors, aretaught without limitation by U.S. Pat. No. 5,206,590, entitled“Magnetoresistive Sensor Based On The Spin Valve Effect,” which ishereby incorporated by reference in its entirety. GMR read-sensors maycomprise other structures having similar functionality. The GMRread-sensors typically have an internal antiparallel pinned layer forincreased sensitivity, as taught without limitation by U.S. Pat. No.5,465,185, entitled “Magnetoresistive Spin Valve Sensor With ImprovedPinned Ferromagnetic Layer And Magnetic Recording System Using TheSensor,” which is hereby incorporated by reference in its entirety. Arecent form of read-sensor, TMR, uses a tunnel barrier layer to augmentthe GMR internal structure and to provide increased sensitivity, astaught without limitation by U.S. Pat. No. 5,764,567, entitled “MagneticTunnel Junction Device With Nonferromagnetic Interface Layer ForImproved Magnetic Field Response,” which is hereby incorporated byreference in its entirety. TMR read-sensors may comprise otherstructures having similar functionality.

In the exemplary embodiment illustrated in FIG. 1, write-head 106 islonger along the X-axis direction than read-sensor 108. The activesensing portion of read-sensor 108 is smaller than write-head 106, alongthe X-axis, as write-head 106 is used to magnetize nanoparticle 212 asdescribed with reference to FIGS. 3 and 4B, for detection ofnanoparticles 212 by read-sensor 108. If read-sensor 108 were too largein the X-axis direction, it could potentially encounter unmagnetizednanoparticles 212 and thus register an undesired false-negativedetection of antigen 210, as described with reference to FIG. 3.

Head-module 104 may be maintained in linear alignment with biosampletracks 180 along the X-axis by position-error-servo (PES) read-head 192,which reads magnetically encoded servo-alignment marks 193 from servotrack 194 on substrate 199. PES read-head 192 may be, for example, anAMR, GMR, or TMR read-sensor. Magnetically encoded servo alignment marks193 are encoded by the manufacturer of substrate 199 on either a pieceof magnetic tape adhered to substrate 199 or encoded on a magneticrecording layer directly deposited on substrate 199. In the exampleillustrated in FIG. 1, particular servo-alignment marks 193 shown inservo track 194 are Timing Based Servo (TBS) servo-alignment marks suchas those used in IBM's Linear Tape Open (LTO) tape drive products, e.g.,IBM tape drive models TS1120™ and TS1130™. TBS servo-alignment marks aretaught without limitation by U.S. Pat. No. 6,320,719, entitled “TimingBased Servo System for Magnetic Tape Systems,” which is herebyincorporated by reference in its entirety. Servo-alignment marks 193 maycomprise other structures with similar functionality. The writing of TBSservo-alignment marks 193 in servo track 194, as shown in FIG. 1, istaught without limitation by U.S. Pat. No. 6,282,051, entitled “TimingBased Servo System for Magnetic Tape Systems,” which is herebyincorporated by reference in its entirety. TBS servo-alignment marks 193may comprise other structures with similar functionality.

FIG. 2 illustrates another exemplary embodiment of servo-alignment marks193 in the form of magnetically-encoded Z-pattern 130 that comprisesservo-alignment marks in servo track 194. Relative to the Y-axis, thedistance between the top and bottom legs of Z-pattern 130 is constantand equal to the sum of line segments AB and BC, which is equal to thesum of line segments A1B1 and B1C1 in path 131. This distance is alsoequal to the sum of line segments A2B2 and B2C2 in path 132, and the sumof line segments A3B3 and B3C3 in path 133. Thus, the velocity of headmodule 104 along the Y-axis relative to substrate 199 may be calculatedby dividing the sum of line segments (AB+BC) by the time to transitZ-pattern 130 by head module 104. This velocity calculation is notaffected by the position of PES read-head 192 along the X-axis, becausethe top and bottom of Z-pattern 130 are both parallel to the X-axis.

The position-error-servo (PES) signal corresponding to the position ofPES read-head 192, and hence write-heads 106 and read-sensors 108, alongthe X-axis may be determined by subtracting the distance AB from thedistance BC each time a Z-pattern 130 is encountered by PES read-head192. As can be seen in FIG. 2, the PES signal from PES read-head 192following path 132 is less than zero because the distance difference(B2C2−A2B2) is less than zero. Similarly, the PES signal from PESread-head 192 following path 131 is greater than zero because thedifference (B1C1−A1B1) is greater than zero. Additionally, the value of(BC−AB) varies linearly as PES read-head 192 moves from left to rightalong the X-axis. Thus the PES signal, as calculated by the differencein distance (BC−AB), provides an X-axis PES signal for head-module 104and its pairs of electromagnetic write-heads 106 and magneto-resistiveread-sensors 108. This PES signal is incorporated into servo controlcircuit 600 shown in FIG. 6.

In an exemplary embodiment of the invention, the value of the linesegment difference (BC−AB) is evaluated based on the time it takes forthe PES read head 192 to cross segments AB and BC when the head-module104 is moving at a constant velocity during its Y-axis seek operation.This is the case where the transit time for the PES read head 192 tocross each Z-pattern 130 is constant. In the exemplary embodiments ofthe invention shown in FIGS. 1 and 2, TBS servo-alignment marks 193 andZ-pattern 130 could be non-magnetic stripes, either lithographed,silk-screened, or ink-jet printed, and read with an optical laser. InFIG. 2, path 133 is the desired path for PES read-head 192 aselectromagnetic write-heads 106 and magneto-resistive read-sensors 108are aligned with biosample tracks 180. With path 133, the distancedifference (B3C3−A3B3) is equal to zero, i.e., line segment B3C3 isequal to line segment A3B3. For path 131, the distance difference(B1C1−A1B1) is greater than zero, which means that head-module 104 mustbe moved in the +X direction by X-axis actuator 606 so thatelectromagnetic write-heads 106 and magneto-resistive read-sensors 108are aligned with biosample tracks 180. The operation of the X-axisactuator 606 is described below with reference to FIG. 6. Similarly, forpath 132, the distance difference (B2C2−A2B2) is less than zero, whichmeans that head-module 104 must be moved in the −X direction by X-axisactuator 606 so that electromagnetic write-heads 106 andmagneto-resistive read-sensors 108 are aligned with biosample tracks180.

FIGS. 1 and 3 illustrate an exemplary analytic device 100, and FIGS. 4Aand 4B illustrate an exemplary analytic process 400, respectively. Instep 404, biosample tracks 180 are deposited on substrate 199 withnonmagnetic materials such as gold, silicon, or SiO₂, and othermaterials having similar magnetic properties. Deposition methods mayinclude photolithography, silk-screening, and other similar processes.As shown in FIG. 1, biosample tracks 180 are deposited in stripes onsubstrate 199 with a track-to-track spacing along the X-axis, matchingthe read-sensor to read-sensor spacing on head-module 104. Then, in step406, antibodies 208A are bonded to biosample tracks 180, for example,via amide, self-assembled-monolayers (SAMS), alkoxysilane, organicfunctional trialkoxysilane, or thiol bonds 206A.

In one example of the bonding of the antibodies 208A to the biosampletracks 180, the bonding may comprise first coating substrate 199 withamide, self-assembled-monolayers (SAMS), alkoxysilane, or thiol and thenplacing a solution of antibodies 208A on substrate 199 and gentlyrocking substrate 199 for a period of time, up to six hours. Amiderefers to organic compounds that contain the functional group consistingof an acyl group, with the chemical notation C═O, linked to a nitrogen(N) atom. A SAM is an organized layer of amphiphilic molecules in whichone end of the molecule, the “head group,” shows a special affinity fora substrate, such as gold, silicon, or SiO₂ biosample tracks 180. At theopposite end of the SAM from the “head group” is a functional group atthe terminal end, and it is to this functional group that antibodies208A are attached in step 406. Lastly, a thiol is a compound thatcontains the functional group composed of a sulfur atom and a hydrogenatom (—SH). Being the sulfur analog of an alcohol group (—OH), thisfunctional group is referred to either as a thiol group or a mercaptangroup.

There are generally five known isotopes (types) of antibodies 208A and208B for mammals. In FIG. 3, the Y-shape of antibodies 208A and 208B arethat of monomer antibodies. There are three isotopes of monomerantibodies: IgD, IgE, and IgG, where the prefix Ig is the symbol forImmunoglobulin. These monomer antibodies each have one unit of Ig. IgDantibodies function mainly as antigen receptors on B cells that have notbeen exposed to antigens. IgD antibodies have been shown to activatebasophils and mast cells to produce antimicrobial factors. B cells arelymphocytes that play a large role in the humoral immune response, asopposed to the cell-mediated immune response, which is governed by Tcells. The principal functions of B cells are to make antibodies againstantigens, perform the role of Antigen Presenting Cells (APCs) andeventually develop into memory B cells after activation by antigeninteraction. B cells are an essential component of the adaptive immunesystem. IgE antibodies binds to allergens and triggers histamine releasefrom mast cells and basophils, and are involved in allergies. In itsfour forms, IgG antibodies provide the majority of antibody-basedimmunity against invading antigens, and thus IgG antibodies are thepreferred antibodies 208A and 208B. IgG antibodies are the only antibodycapable of crossing the placenta to give passive immunity to fetus.

In an exemplary embodiment of the invention, the base of the stem in aY-shaped monomer antibody 208A is bonded to biosample tracks 180 viaamide, SAMS, alkoxysilane, organic functional trialkoxysilane, or thiolbonds. There is only one isotope of a dimer antibody, IgA, which has twoIg units. IgA antibodies can be found in mucous membrane areas, such asthe gut, respiratory track, and urogenital track, as well as in saliva,tears, and maternal milk. Lastly, there is only one isotope of pentamerantibody, IgM, which has five Ig units. IgM antibodies are expressed onthe surface of B cells. IgM antibodies eliminate antigens in the earlystages of B cell humoral immunity before there are sufficient IgGantibodies in a person's body.

Other analytes may have different antibodies, such as the tetramericantibody with four Ig units, an example of which is the IgM found in theteleost fish. Thus, analytic process 400 applies to biological analysesin medical and veterinary medicine, as well as to other biologicalapplications. In the exemplary embodiments of the invention,nanoparticles 212 may be bonded to any biological matter and steps inanalytic process 400 may be used to track and identify antigens presentin a sample of the biological matter.

In the illustrated embodiment of analytic process 400, step 408comprises rinsing substrate 199 with water such as distilled water orother rinsing agent, which may have its surface tension reduced via avery mild surfactant such as a mild detergent solution. The rinsingremoves any antibodies 208A that are not specifically bonded to analytictracks 180. After rinse step 408, antibodies 208A are exposed toantigens 210 in step 410. In one example, this may be accomplished byplacing a blood sample or other biological sample on substrate 199 andthen gently rocking substrate 199 for a period of time, up to six hours.Antigens 210 may comprise cancer cells, viruses such as Human PapillomaVirus (HPV), or bacteria. Human Papilloma Virus can lead to infectionsand cancers of the human reproductive organs. Antibodies 208A arespecifically chosen based on the targeted antigens 210.

In step 410, antigens 210 are bonded to monomer antibodies 208A atantigen receptors 209A which are diagrammatically shown to be at thev-shaped end of antibodies 208A. Each monomer antibody 208A has twoantigen receptors 209A. Step 410 may include repetitive rocking ofsubstrate 199 to facilitate the bonding of antigens 210 and antibodies208A at antigen receptors 209A. Then, in step 412, another rinse isperformed on substrate 199 with water such as distilled water or otherrinsing agent, which may have its surface tension reduced via a verymild surfactant such as a mild detergent solution. Step 412 is analogousto step 408, but this time for removing antigens 210 not bonded toantibodies 208A.

In parallel with steps 404, 406, 408, 410, 412 is the creation ofnanoparticle-labeled antibodies in steps 414, 416, 418, 420, and 422 ofthe illustrated analytic process. In step 414, magnetic inner cores,shown as inner core 216 in FIG. 2, may be heated above their Curietemperature to demagnetize the inner cores. The demagnetization keepsthe nanoparticles that comprise the inner cores as individual particlesby mitigating the forming of lumps which magnetized nanoparticles areprone to form. Magnetic inner cores 216 may comprise hard magneticmaterials with high coercivity, such as Fe₂O₃, CrO₂, and Barium FerriteBaFe. As examples, magnetic inner cores 216 may comprise iron oxidebased nanoparticle materials, including M Fe₂O₄ (where M may be Co, Ni,Cu, Zn, Cr, Ti, Ba, or Mg) nanomaterials, and iron oxide coatednanoparticle materials or other structures with similar functionality.The forming of such nanoparticles is taught without limitation by U.S.Pat. No. 6,962,685, entitled “Synthesis of Magnetite Nanoparticles andthe Process of Forming,” which is hereby incorporated by reference inits entirety. Then, in step 416, the heated magnetic inner cores 216 areallowed to cool. Steps 414 and 416 are optional steps, as themanufacture of inner cores 216, which may include high temperaturesintering, may render inner cores 216 demagnetized during themanufacturing process.

Following step 416, step 418 may comprise coating inner cores 216 withan outer-shell 214, for example, of nonmagnetic gold, silicon, or SiO₂,to create nanoparticles 212. The step of coating the inner cores 216with outer-shells 214 is analogous to creating biosample tracks 180 instep 404. Then, in step 420, antibodies 208B are bonded to nanoparticles212 via amide, self-assembled-monolayers (SAMS), alkoxysilane, organicfunctional trialkoxysilane, or thiol bonds 206B. This bonding isanalogous to bonding antibodies 208A to biosample tracks 180 in step406. The bonding of the antibodies 208B may be accomplished by firstcoating nanoparticles 212 with amide, self-assembled-monolayers (SAMS),alkoxysilane, organic functional trial koxysilane, or thiol and thenplacing nanoparticles 212 in a solution containing antibodies 208B andgently rocking this solution for a period of time, up to six hours.Antibodies 208A and 208B are biologically identical, as both bond to thesame antigen 210. Following step 420, step 422 comprises rinsingnanoparticles 212 with water, such as distilled water, or other rinsingagent, which may have its surface tension reduced via a very mildsurfactant such as a mild detergent solution to remove unbondedantibodies. The rinsing step 422 is analogous to the rinsing step 408above. At the conclusion of both steps 412 and 422, process 400converges at step 424 and continues with step 430 in FIG. 4B.

In step 430, antigens 210 are exposed to nanoparticles 212 which haveantibodies 208B bonded to them. This may be done by placing a solutionof nanoparticle-labeled antibodies 208B on substrate 199 and then gentlyrocking substrate 199 for a period of time, up to six hours. Antigenreceptors 209B of antibodies 208B bond with antigen 210. Step 432comprises rinsing substrate 199 with water, such as distilled water, orother rinsing agent, which may have its surface tension reduced via avery mild surfactant such as a mild detergent solution. The rinsing instep 432 removes any nanoparticles 212 not bonded to an antigen 210 andis analogous to step 408. If substrate 199 is a Peltier substrate, inoptional step 434, a DC voltage of a first polarity may be applied tothe Peltier substrate, to heat surface 208 and hence dry both biosampletracks 180 and biological sample 206A-208A-210-208B-206B-212. Then, inoptional step 436, a DC voltage of a second and opposite polarity, maybe applied to the Peltier substrate, to cool surface 203 and hence coolboth biosample tracks 180 and biological sample206A-208A-210-208B-206B-212. Heat sink 200 may be used to dissipateexcess heat generated by the Peltier substrate along surface 201.

In the exemplary embodiment of the analytical process of the inventionshown in FIG. 4B, scan step 438 involves moving head-module 104 linearlyin the +Y direction relative to substrate 199, which could equally bedone by moving substrate 199 linearly in the −Y direction relative tohead-module 104. In previous step 414, inner cores 216 weredemagnetized. Now, in step 438, write-head 106 writes to nanoparticles212 to magnetize inner cores 216. Write-head 106 may write with aconstant “DC” magnetic polarity for the duration of scan steps 438 and440, so that there are no unwritten regions of substrate 199. Then inread-after-write step 440, read-sensor 108 detects the freshlymagnetized inner cores 216 of nanoparticles 212, and hence detectingantigens 210 because nanoparticles 212 are bonded to antibodies 208B,which in turn are bonded to antigens 210. The adjacent logical-steps 438and 440, as well as the physical proximity of write-head 106 andread-sensor 108 in a typical electromagnetic head module, provide anadvantage when using tape drive products to detect antigens. The innercores 216 of nanoparticles 212 are magnetized by write-head 106 alongthe Y-axis, in what is called longitudinal-recording in the tape driveindustry. This is the same direction that read-sensor 108 magneticallydetects nanoparticles 212. As a result, the nanoparticles 212 may bemagnetized by write-head 106 and then magnetically detected byread-sensor 108 in the same scan of the biosample tracks 180. Magneticshield 107 separates write-head 106 and read-sensor 108 so that there isno meaningful cross-talk between write-head 106 and read-sensor 108during steps 438 and 440.

As an alternate embodiment of the invention, once steps 438 and 440 arecompleted by moving head-module 104 linearly in the +Y directionrelative to substrate 199, write-head 106 may be turned off asnanoparticles 212 are now magnetized. Step 440 may be repeated multipletimes across biosample tracks 180 along both the +Y and −Y directionsduring which read-sensor 108 repeatedly checks for magnetizednanoparticles 212 and hence detecting antigens 210. The multiple readoperations insure that all antigens 210 on biosample tracks 180 aredetected. As described above with reference to FIG. 1, the antigens 210are attached to nanoparticles 212 through antibodies 208A and 208B.

In another exemplary embodiment of the invention where there are morebiosample tracks 180 than write-head 106 and read-sensor 108 pairs inhead-module 104, head-module 104 may scan the biosample tracks 180 in aserpentine pattern. The head-module 104 performs a scan in the +Ydirection, as head-module 104 only provides read-after-write capabilityin the +Y direction as illustrated in FIG. 1. Then a second head-modulecomprising a mirror image of head-module 104 may perform aread-after-write operation in the −Y direction.

The coercivity of a magnetic inner core 216 may be selectively chosen tohave any of various values, depending upon the antigen 210 to bedetected. The nanoparticles 212 with magnetic inner cores 216 ofdifferent coercivity values may be respectively bonded to differenttypes of antibodies 208A and 208B to detect a various types of antigens210 on the substrate 199 at the same time. A nanoparticle 212 thus mayhave different magnetic properties associated with each antigen-antibodycombination. Read-sensor 108 detects the different magnetic propertiesof inner core 216 based on different materials used for that inner core,for example, Fe₂O₃, CrO₂, BaFe, M Fe₂O₄ (where M may be Co, Ni, Cu, Zn,Cr, Ti, Ba, or Mg), or other structures with similar functionality.Read-sensor 108 thus could detect different antigens 210 on the samescan of the biosample tracks 180, per steps 438 and 440 in FIG. 4B. Tofacilitate the detection of nanoparticles of different magneticproperties and hence the detection of different types of antigens,calibration of read-sensor 108 may be performed according to anexemplary calibration process 500 illustrated in FIG. 5.

Calibration of Read-Sensors

Referring to FIG. 5, in one exemplary embodiment of the calibration ofread-sensor 108, calibration process 500 begins at step 502 and proceedswith step 504, where a first “DC” bias current (I0+I1) is applied toread-sensor 108. This first bias current may consist of an offset DCcurrent I0 plus a DC current I1. In succeeding step 506, the process 500measures resistance R1 of read-sensor 108 while DC current (I0+I1) isapplied. In step 508, second DC bias current I2 may be applied toread-sensor 108, where I2=I0−I1. In steps 506 and 508, offset current I0is typically zero milliamperes, but may have a positive or negativevalue. In succeeding step 510, the calibration process 500 measuresresistance R2 of read-sensor 108 while DC current I2 is applied, whereI2=I0−I1. Then in step 512, a determination is made whether resistanceR1 or R2 exceeds threshold resistance R0 and thus indicating anon-operational read-sensor 108. If resistance R1 or R2 exceeds thethreshold, then process 500 branches to step 524 where a message isdisplayed to the user to replace head-module 104 as the read-sensor 108,which is an integral part of head-module 104, may be non-operational. Ifneither resistance R1 nor resistance R2 exceeds the threshold per thedetermination in step 512, then process 500 branches to step 514 andcalculates resistance R3, where R3=R1−R2.

In step 516, calibration process 500 calculates a bias current I3, whereI3=I1*(R_calibrate/R3) and R_calibrate is a preset value maintained byprocessor 602 shown in FIG. 7. In step 518, calibration process 500applies bias current I3 to read-sensor 108 when performing step 440 aspart of the bio-assay process 400. In step 520, a determination is madewhether calibration time T exceeds a time threshold T0, where T is thetime elapsed during the calibration steps 504 to 518. If time T has notexceeded the threshold T0, then calibration process 500 cycles back tostep 520 and continues checking time T against the threshold T0.Otherwise, process 500 resets time T to zero in step 522 beforereturning to step 504 to begin the calibration process again. Process500 is executed by processor 602, as described below with reference toFIG. 7.

Mitigation of Corrosion in Head-Module

When read-sensor 108 is not in use for detecting magnetizednanoparticles 212, in one exemplary embodiment of the invention, acurrent may be passed through read-sensor 108 in order to mitigatecorrosive effects of ambient air. This current may be, for example, adirect current in the range of three to seven milliamperes. Alternately,the current may be a pulse-width-modulated (PWM) direct current oralternating current (AC) having an amplitude of, for example, three toseven milliamperes. This current causes read-sensor 108 to besufficiently warm to minimize corrosive effects of water vapor,chlorine, and other gases present in ambient air in the vicinity of thebiosample tracks 180. In one exemplary embodiment of the invention, thiscurrent may be applied based on signals sent by processor 602 to a poweramplifier 716, as illustrated in FIG. 7. The power amplifier 716supplies electric power to Wheatstone Bridge 706, where read-sensor 108is a component of the Wheatstone Bridge 706.

Read-sensor 108 is essentially an impedance device, such as a resistor,which exhibits a change in resistance when exposed to a magnetic field.In the illustrated exemplary embodiment of the calibration, process 500assumes that read-sensor 108 responds linearly when not saturated by theapplied magnetic field, and to a first order approximation, read-sensor108 does respond linearly. Correlation coefficients of up to 99.9% havebeen empirically measured, regarding the change in resistance inread-sensor 108 versus applied magnetic field, indicating a sufficientlyhigh degree of linearity for application of calibration process 500.

Per Ohm's law, V=IR, voltage and current are directly proportional toeach other in read-sensor 108. Thus, as an alternate embodiment ofcalibration process 500, first and second voltages V1, V2 could be usedto obtain the first resistance R1 and second resistance R2,respectively, without loss of generality.

A Servo Control Circuit

FIG. 6 shows an exemplary embodiment of a servo control system 600 forcontrolling the X-axis and Y-axis motion of head-module 104. As anexample, FIG. 6 shows one biosample track 180, and one pair ofwrite-head 106 and read-sensor 108. Processor 602 receivesposition-error-servo (PES) signals from PES read-head 192 when PESread-head 192 reads servo-alignment marks 193 in servo track 194. Basedon this PES information, processor 602 sends a signal to power amplifier604 to control X-axis actuator 606 which in turn controls the motion ofhead module 104 in the X-axis direction. With X-axis actuator 606connected to head-module 104 via mechanical connector 608, head-module104 may be positioned to center write-head 106 and read-sensor 108 onbiosample track 180. Processor 602 may send signals to power amplifier614 to control Y-axis actuator 610 for conducting a scan by head module104 across substrate 199. With Y-axis actuator 610 connected to X-axisactuator via mechanical connector 612, head-module 104 can be movedalong the Y-axis in a controllable manner.

As an example, when a predetermined number of servo-alignment marks 193are read by PES read-head 192, processor 602 stops the Y-axis motion ofhead-module 104. A servo-system for control of X-axis actuator 606 andhead-module 104 along the X-axis direction, particular toservo-alignment marks 193 shown in servo track 194 in FIG. 1, is taughtwithout limitation by U.S. Pat. No. 5,689,384, entitled “Timing BasedServo System for Magnetic Tape System,” which is hereby incorporated byreference in its entirety. The servo-system may comprise otherstructures with similar functionality. As previously described regardingZ-pattern 130, the velocity of head module 104 relative to substrate 199along the Y-axis can be calculated by dividing distance AB+BC by thetime it takes for head module 104 to transit Z-pattern 130. Thisvelocity measurement can be used by processor 602 to control Y-axisactuator 610 to keep head module 104 at a constant Y-axis velocity Vyrelative to substrate 199. The position along the Y-axis of head module104 relative to substrate 199 can be obtained by countingservo-alignment marks 193 or Z-pattern 130 by PES read-head 192 andprocessor 602.

A Write and Read Circuit

FIG. 7 shows an exemplary embodiment of a write and read circuitry 700for writing to the biosample tracks 180 (i.e., for magnetizingnanoparticles 212) and reading from the biosample tracks 180 (i.e., forsensing and detecting the magnetized nanoparticles 212). Processor 602may send signals to power amplifier 704 which provides power towrite-head 106 for magnetizing nanoparticles 212. Processor 602 mayfurther send signals to power amplifier 716 which powers Wheatstonebridge 706. Read-sensor 108 is one component in Wheatstone bridge 706and thus receives DC current from Wheatstone bridge 706. Wheatstonebridge 706 serves the function of balancing out the zero-magnetismresistance of read-sensor 108 so that only the change in resistance ofread-sensor 108 is passed onto amplifier 714. Such resistance change isdue to the detection of a magnetized nanoparticle 212, which is sent toamplifier 714 and filter 718 before being received by processor 602.

Filter 718 filters out 60 Hz noise, which is pervasive noise in anoffice or laboratory with lighting where processes of the invention aretypically performed. Processor 602 makes the determination of whether ananoparticle 212 was detected, and hence an antigen 210 being detected.The change in resistance of read-sensor 108 is directly proportional tothe magnetic field provided by nanoparticle 212, which may havedifferent coercivities depending upon whether inner core 216 is Fe₂O₃,CrO₂, BaFe, M Fe₂O₄ (M=Co, Ni, Cu, Zn, Cr, Ti, Ba, Mg), etc. Inaddition, particular antibodies 208A and 208B could be associated withinner cores 216 of nanoparticles 212 having a given coercivity. As aresult, processor 602 could register the detection of different antigens210 during steps 438 and 440 of process 400 depending on correspondingcombinations of antibodies 208A and 208B and nanoparticles 212. Theidentification of the various antigens 210 simultaneously on the samebiosample track 180 may be facilitated by a lookup table 720 inprocessor 602. In one exemplary embodiment of the invention, the lookuptable 720 contains a list of (a) antigens 210, (b) the antibodies 208Aand 208B used for bonding antigens and nanoparticles, and (c) thecoercivity of the inner cores 216 of nanoparticles 212 bonded to theantibodies 208B.

Correlation of Detection Results

In another embodiment of the invention, a correlation calculation may beperformed by the write and read circuit of FIG. 7 to improve theaccuracy of the detection of magnetized nanoparticles 212. Referring toFIGS. 3, 4A, 4B, 6 and 7, processor 602 performs correlation calculationC(y) in equation [1] between a detection signal profile g(y) read byread-sensor 108 when a nanoparticle 212 is detected and a matchedfilter. The matched filter comprises an impulse response h(y) of anideal signal profile of a detected nanoparticle. Since h(y) is usedrepetitively, it may be calculated once and stored as matched filter 730in processor 602. In equation [1], η is the integration variable alongthe Y-axis as read-sensor 108 scans along the Y-axis.C(y)=∫g(η)h(η−y)dη  Equation [1]

The range of correlation C(y) is between −1 and +1, where −1 representsthe ideal correlation of one hundred percent (100%). The electricalwaveform g(y) of each potential detection of a nanoparticle 212 byread-sensor 108 has its correlation C(y) calculated in step 442 of FIG.4A. Processor 602 then compares this correlation C(y) against athreshold correlation value C0 before accepting the signal g(y) as avalid detection of a nanoparticle 212. This correlation removes spuriouselectrical noise from actual detections of nanoparticles, and thusmitigates false-positive detections of antigens. In step 444 of FIG. 4B,the results of a scan may be displayed to a physician or clinician toinform the physician or clinician of the presence (or absence) of targetantigens in the biological sample. The results may include items such asthe antigen(s) tested for, the types of antibodies used, a simplepositive-detection or negative-detection indication for each antigen,the number of nanoparticles counted for each antigen to give anindication of the prevalence of the targeted antigen, and the number ofrejected detections based on the correlation calculation of step 442. Inaddition, the results may include patient name, date of test, time oftest, and name of attending doctor or clinician. Process 400 ends atstep 446 in FIG. 4B.

Those of skill in the art will understand that changes may be made withrespect to the exemplary embodiments described above, including, but notlimited to, changes to the ordering of the steps. Further, those ofskill in the art will understand that differing specific componentarrangements may be employed than those illustrated herein.

While the exemplary embodiments of the invention have been illustratedand described in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the invention.

What is claimed is:
 1. A circuit for controlling a head module to detectantigens from a biosample track, the head module having aposition-error-servo (PES) read sensor for reading Z-patternservo-alignment marks along the biosample track, the circuit comprising:a processor for: receiving position-error-servo signals from the PESread sensor as the head module moves along the biosample track,determining from the position-error-servo signals a first distance alongthe direction of the biosample track between a bottom line of theZ-pattern to the diagonal line of the Z-pattern, determining from theposition-error-servo signals a second distance along the direction ofthe biosample track between the diagonal of the Z-pattern to a top lineof the Z-pattern, and determining a position of the head module in adirection perpendicular to the biosample track from a difference betweenthe first distance and the second distance; an electromagnetic writehead for magnetizing a plurality of nanoparticles labeling the antigens;a magneto-resistive read sensor for detecting the antigens via thenanoparticles, the write head and the read sensor being part of the headmodule; and a plurality of actuators coupled to the head module forcontrolling the motion of the head module based on theposition-error-servo signals.
 2. The circuit of claim 1, wherein theactuators comprise an X-axis actuator for controlling the head module inthe direction perpendicular to the direction of the biosample track andan Y-axis actuator for controlling the head module in the direction ofthe biosample track.
 3. The circuit of claim 2, wherein the processorsends a signal to the X-axis actuator to center the write head and theread sensor on the biosample track based on the servo-alignment marks.4. The circuit of claim 3, wherein the processor sends the signal to theX-axis actuator through a power amplifier coupled to the X-axisactuator.
 5. The circuit of claim 2, wherein the processor sends asignal to the Y-axis actuator to perform a scan by the head modulelinearly in the direction of the biosample track.
 6. The circuit ofclaim 5, wherein the processor sends the signal to the Y-axis actuatorthrough a power amplifier coupled to the Y-axis actuator.
 7. The circuitof claim 2, wherein the processor sends a signal to the Y-axis actuatorto stop the motion of the head module in the direction of the track inresponse to the PES read sensor reading a predetermined number ofservo-alignment marks.
 8. The circuit of claim 1, wherein the processorcalculates the velocity of the head module based on predeterminedsegments in the Z-pattern and transit time of the head module across thesegments.
 9. The circuit of claim 8, wherein the processor controls theY-axis actuator to maintain the head module at a constant speed relativeto the biosample track based on the calculated velocity.
 10. The circuitof claim 1, wherein the head module is maintained in linear alignmentwith the biosample track based on the servo-alignment marks.
 11. Thecircuit of claim 1, wherein the servo-alignment marks are on a servotrack parallel to the biosample track.
 12. The circuit of claim 1,wherein the position of the head module along the biosample track isdetermined based on the number of the servo-alignment marks read by thePES read sensor.
 13. The circuit of claim 1, wherein the servo-alignmentmarks are timing based servo (TBS) marks.
 14. A system for detectingnanoparticle-labeled antigens, comprising: a biosample track depositedon a magnetic tape media and having the nanoparticle-labeled antigensattached thereon; a head module having a position-error-servo (PES) readsensor for reading Z-pattern servo-alignment marks along the biosampletrack, an electromagnetic write head for writing to the tape media tomagnetize the nanoparticles, and a magneto-resistive read sensor forreading the tape media to detect the antigens via the nanoparticles; anda circuit for controlling the head module, the circuit comprising aprocessor for receiving position-error-servo signals from the PES readsensor as the head module moves along the biosample track, determinefrom the position-error-servo signals a first distance along thedirection of the biosample track between a bottom line of the Z-patternto the diagonal line of the Z-pattern, determine from theposition-error-servo signals a second distance along the direction ofthe biosample track between the diagonal of the Z-pattern to a top lineof the Z-pattern, and determine a position of the head module in adirection perpendicular to the biosample track from a difference betweenthe first distance and the second distance, an X-axis actuator forcontrolling the head module in the direction perpendicular to the track,and an Y-axis actuator for controlling the head module in the directionof the track.
 15. The system of claim 14, wherein the head module andcircuit are part of a magnetic tape drive.
 16. The system of claim 14,wherein biosample track is deposited on a substrate and the head modulemoves relative to the substrate linearly in the direction of thebiosample track during the writing and reading of the tape media. 17.The system of claim 16, wherein the head module is stationary and thesubstrate is swept across the head module linearly in the direction ofthe biosample track during the writing and reading of the tape media.18. The system of claim 14, wherein the head module is a helical-scanrotary head and the biosample track is deposited on a flexible mediamoving at an angle to the Y-axis of the helical-scan rotary head. 19.The system of claim 14, wherein the PES read sensor is selected from thegroup consisting of an anisotropic magneto-resistive (AMR) read sensor,a giant magneto-resistive (GMR) read-sensor, and a tunnelmagneto-resistive (TMR) read-sensor.
 20. The system of claim 14, whereinthe servo-alignment marks are timing based servo (TBS) marks.
 21. Thesystem of claim 14, wherein the servo-alignment marks are magneticallyencoded on a substrate on which the biosample track is deposited. 22.The system of claim 14, wherein the servo-alignment marks aremagnetically encoded on a magnetic tape adhered to a substrate on whichthe biosample track is deposited.
 23. The system of claim 14, whereinthe servo-alignment marks are magnetically encoded on a magneticrecording layer deposited on a substrate on which the biosample track isdeposited.